Existing systems attempt to model business processes or other real-world interactions between autonomous agents via high-level workflows. However, the workflows may vary in a variety of dimensions such as (a) execution and modeling complexity, (b) knowledge of the structure of the flow at design time, (c) statically defined or ad-hoc/dynamic, (d) ease of authoring and editing the flow at various points in its lifecycle, and (e) weak or strong association of business logic with the core workflow process. Existing workflow models fail to accommodate all these factors.
Further, most existing workflow models are based on either language-based approaches (e.g., BPEL4WS, XLANG/S, and WSFL) or application-based approaches. Language based approaches are high-level workflow languages with a closed set of pre-defined constructs which help model the workflow process to the user/programmer. The workflow languages carry all of the semantic information for the closed set of constructs to enable the user to build a workflow model. However, the languages are not extensible by the developers and represent a closed set of primitives that constitute the workflow model. The languages are tied to the language compiler shipped by the workflow system vendor. Only the workflow system product vendor may extend the model by extending the language with a new set of constructs in a future version of the product. This often requires upgrading the compiler associated with the language. In addition, the languages usually do not declaratively expose or define functions or operations that can be readily and efficiently used by other programs.
Application based approaches are applications that have the workflow capabilities within the application to solve a domain specific problem. These applications are not truly extensible nor do they have a programmable model.